A Tail or Two
by Meer-Katnip
Summary: A kraken, hefty amounts of explosives, and a very unlikely friendship, although not necessarily in that order. Throw together and mix for maximum impact.


**If _Full Moon, Full Moon_ was a really weird _Survival_ AU, then this is basically an equivalent for _Dragonfire._ I seem to have a weird obsession with doing this sort of cracky thing. *puzzled shrug***  
 **As usual, I own a grand total of nothing, and the only profit I make from this sort of thing are reviews, which are pretty much the only things that give me joy nowadays, apart from chocolate cake, Undertale, and new Big Finish releases.**

* * *

It was half past eight in the morning on the small, mostly uninhabited island that was the perfect place for scientific research.

The Doctor was taking samples in the shallow water around the bay area, and considering if there would be enough time for a quick cup of tea before he got to work with analysis when the water a few metres away from him bubbled and fizzed. The shimmer of fins was just barely visible, flashing past, and then everything stilled again.

The Doctor stopped, put down his equipment, and stared into the depths. He nearly dismissed the whole experience as a figment of the imagination, or a trick of the light, when a girl's head popped out of the water; cheeks flushed and wet brown hair flopping over her eyes.

"I'm being chased by a sea monster," she gasped. "and- oh _shit, sorry-_ "

She ducked back under the water again, making droplets of water cascade everywhere. In a heartbeat, she re-emerged again, this time a bit closer to shore. "Have to keep moving," she explained, with an annoyed roll of her eyes. "Otherwise, Tentacles down there'll get me, and I'll be sushi." She bobbed up and down for a moment. "I'm Ace, by the way."

"A pleasure, I'm sure," said the Doctor, sitting down on a rock. "I'm generally known as the Doctor. Is there anything I can do to help?"

Ace nodded enthusiastically, and emerged a bit further from the water. She was wearing a bulky black jacket, covered in various pins and badges that probably didn't help her swimming abilities much. "Here," she said, digging around in her pockets. "Take this." She produced a silver canister and tossed it in his direction. It landed in the water, and the Doctor leaned out to fish it out. "The timer's about ten seconds, but it could be less. Chuck it over at Tentacles when he comes closer- it should scare him off well and good."

The water churned alarmingly, several metres behind her, and she glanced back with a nervous twitch of her head. "I'll go lure it over."

"Good luck," said the Doctor with a raised eyebrow. Ace grinned, ducking into the water once again, just as a massive head erupted up from the deep, aiming directly where she had been only moments before. It was draconian in form, and its mouth was lined with rows of razor-sharp teeth which gnashed at the air. For some inexplicable reason, its eyes were glowing red.

It thrashed back and forth for a second, and fell back into the water, sending large waves crashing over most of the bay. Under the surface, the rest of its body was muscled and resembled a snake's, albeit a massive, killer snake with fins, tentacles, and a forked tail that could rival a whale's.

The Doctor eyed the silver canister in his hands for a moment, then shrugged and adjusted his hat.

"Oi, seaweed brain!" came Ace's cry from the water beneath him. "Over here!" The monster coiled itself under the surface and shot directly towards her. She dived again, swimming frantically to the side. "Now!"

The Doctor twisted the lid of the canister (having worked out exactly what it was several minutes before) and dropped it almost delicately into the water just ahead of the sea monster. It hit the water with a small splash, and for a moment it seemed as if nothing had happened.

And then there was a massive, echoing explosion that made the water burst in all directions, splashing over everything, and soaking the Doctor to the skin. The monster, below, howled loudly, and took off as fast as it possibly could in the opposite direction.

"Wicked!" gasped a voice after the water had died down a bit, and the Doctor leaned down from his rock to see that Ace was bobbing in the shallows once more. "The timer was a bit off- I need to work on that, actually- but-"

"What was that?" the Doctor interrupted with a glance in the direction that the monster had taken.

"What, the monster or the nitro?" Ace asked brightly, flicking her hair back and out of her eyes. "The explosive's my own recipe. I call it Nitro-Nine. Works best on big honking monsters bent on eating teenage rebels like me."

The Doctor, despite himself, began to smile. "And the monster?"

"Ah," she said. "That would be a kraken."

"As in, the mythical beast that isn't supposed to actually exist?"

"Yes, well," Ace said. "Not so mythical anymore, it looks like."

"They're not exactly on the protected species list," he said wryly. "I don't think any animal protection agencies will be on our case about that, so that's one less thing to worry about."

"What a relief," Ace said sardonically, and smiled. "Thanks for that, though. Don't think I could've taken care of that on my own."

"It was a pleasure to help," replied the Doctor solemnly, inclining his head. "May I have the further pleasure of sharing my morning tea with you? You do look rather hungry, and I know for a fact that monster hunting is a strenuous business."

"Aha," said Ace, and suddenly looked acutely uncomfortable. "There may be a slight problem there."

"How so?"

In response, Ace swam out from the rock a bit, which had, up until now, provided cover for the lower half of her body. Her black jacket dragged a bit in the current as she poked her tail out of the water, and wiggled it slightly. It was a deep, dark blue, with a forked end that thinned out into nothing. It was well-muscled, and the scales along it were perfectly laid, without a single imperfection. It shone in the sunlight. It was out of place and strange to look at, but it was still there.

"I'm a mermaid," she said, a bit needlessly, and managed to look apologetic about it, which was quite the accomplishment. "Ah… please don't freak out?"

* * *

It was easy to reach a compromise. There was a part of the beach where the rocks met a rather deep part of the sea, and there was a minimum of wind and sea spray in that area. As such, it was the perfect place for the Doctor and Ace to have an impromptu picnic. And so they did- with Ace perched comfortably in the shallows, tail twisted beneath her, and the Doctor just above.

"I've never heard of a mermaid colony in this area of the ocean," commented the Doctor.

Ace chewed on a sandwich contemplatively. "You wouldn't have," she said, swallowing. "They're kind of subdued, as far as mermaids go. Well, they try to be anyway."

"'They?" he asked curiously. She bit her lip, and twisted her tail under the water.

"I was kind of… thrown out," she confessed. "I'm not 'one of the pack' anymore."

He leaned back against the rock. The sun was coming out from behind the clouds, setting the water off so it sparkled like diamonds. "What did you do to deserve that?"

"Blew up the art department," Ace said casually, hand shooting out to grab a scone. "Mm. These are good."

"You blew up the art department?" repeated the Doctor, eyebrows shooting up. "Underwater?"

"Yeah, your point is?"

He shook his head slowly and incredulously. "Impressive. Is there anywhere you've got to go, or have you just been wandering around since then?"

"Mainly wandering," she replied. "I have absolutely no idea where any other colonies might be, though, and it's really boring without anyone to talk to. You're the first decent company I've had in _weeks._ " A wry grin flitted over her face. "Apart from ol' Tentacles out there, I mean. And sea monsters don't do 'conversation' very well."

"I can see that," agreed the Doctor. "Er… how does a mermaid come across the ingredients to make high-powered explosives in the middle of the sea?"

"The Bermuda Triangle," Ace informed him. "It actually picks up a lot of useful stuff, and it's not as dangerous if you approach it from underneath." She plucked at her jacket. "It's where I got this."

He shook his head again, but a smile was spreading slowly across his face. "Ace… you are extraordinary."

She froze instantly, with a startled expression, and the Doctor furrowed his brow. "Did I say something wrong?"

She opened her mouth, perhaps to respond, but was interrupted by the distinctive and unmistakable sound of a kraken crashing into the bay. Ace, somewhat instinctively, dived into the water, hit her head on the shallow rocks below, and popped up five seconds later, swearing quite spectacularly.

"Language," the Doctor chided, standing up with easy grace. He brushed at his lapels. "You don't happen to have any more explosives on you?"

Ace winced, pressing a hand to her head. "Um, no. That was my last can. I was going to- never mind, doesn't matter now. Any ideas, Professor?"

He raised an eyebrow at the unexpected nickname, but decided to ignore it for now. "As a matter of fact, yes."

"Great," Ace began, but cut herself off as several hundred kilograms worth of sea monster slammed into the rocks, inches away from her. She yelped, and swam quickly to the other side of the bay. "I'll hold it off again!" she yelled, teeth gritted in determination. "You… I dunno, do something clever. You look like the sort!"

The Doctor scrambled over to his box of tools back on the sand, and started to paw through it frantically. "The sort to do what?" he called over the sounds of hissing and waves crashing at high velocity.

"The sort to do clever things!" Ace gasped between short strokes underwater. She seemed to be focusing almost entirely on remaining streamlined to increase her speed, which was probably a good idea considering the size and strength of the animal chasing her. "I've met blokes like you! You all have this- well, air of authority and superiority!"

"'Authority and superiority'?" the Doctor echoed in mock offence, hastily plugging circuits together and twisting wires so they connected. He hunted through the box for a battery, frowning. "You're acting as if I have some form of god complex!"

There was no response from her, and he briefly glanced over his shoulder in concern. "Ace?"

The water was just calming from the latest splash, and the surface was almost completely undisturbed, which probably meant that both Ace and the kraken were underwater. The Doctor allowed his concentration to drift back to his makeshift machine long enough for him to place the finishing touches on it. He held it up to the early morning sun, and nodded with approval. It wasn't much, but it would do for the purpose it had been created.

Slamming his toolbox shut, he crossed back to the shore just as Ace re-emerged from the water, spitting seaweed out of her mouth with a cross expression on her face. He waved to get her attention, and she shot him a quick thumbs-up, and swam in his direction.

"Done?" she asked, and he handed her his creation- a small metal box with a switch rigged up to it. She eyed it with slight apprehension, and he hastened to explain.

"It transmits a disrupting signal that deters creatures of the species, similar to an EMP," he said, as quickly as he could. "It won't last too long in aquatic conditions, but it should be enough to get rid of it."

She accepted it with a nod. "Got it. Just flick the switch, yeah?"

"Exactly," he said. "Five seconds should do it. You'll need to get rather close, unfortunately."

"No problem," she said, and tucked the box under her arm. "See you in a minute!"

And she was off, swimming forwards quickly and gracefully, darting under waves and in the direction of the kraken. Her tail flashed in the sunlight as she circled it once, holding the box in the air- away from the bulk of the sea spray. The kraken screamed in protest, the sound echoing deep from its massive throat, and began to thrash. The water foamed up; making it near-impossible to see what was going on.

Then there was a triumphant cry from Ace, and the monster bolted- for good this time, it seemed. It left a bubbling, fizzing trail in its wake as it disappeared over the horizon.

"I think I broke it," she said apologetically as soon as she reached the Doctor again. She placed the device- none too gently- onto the rocks, and positioned herself against them so she could begin fiddling with her hair, which was dishevelled, messy, and a waterlogged mess.

"That's perfectly fine," he replied, giving it a perfunctory glance. Its inner circuits were soaked and probably useless. "I wasn't planning on using it for anything useful."

She fished in her jacket pocket, and produced a black scrunchie which she used to tie her hair back into a ponytail. She shook her head to straighten it out, and little droplets of water scattered everywhere. "Actually- is there any reason why you had the equipment to make that thing? Were you expecting to find a kraken here, or are you just the sort of person who carries everything around with them?"

He paused, picked up the device, paused again, put it down, and eventually compromised by sitting down on the rock next to it. "I am, but… yes, I was expecting to find one."

"Oh." Ace bit her lip. "Er… why?"

He sighed and adjusted his hat. "I've been tracking this particular one for several weeks. It's not so much a kraken, really. It's more like a giant robot built vaguely in the shape of one."

"So… it's not alive?"

"Not as such, no."

"Oh," she said again, and looked a bit puzzled. "Why are you chasing it?"

After a moment's deliberation and a barely perceptible nod to himself- because Ace seemed like a very nice person despite her slightly violent tendencies- the Doctor dug into his pockets, and pulled out a map- crinkled and yellow, and held it out so she could see. "It's supposed to be guarding a 'fabulous treasure', apparently."

"Treasure hunting?" she asked, scanning it. "Sounds ace. What's so fabulous about it, then?"

"I have absolutely no idea," he said. "Presumably you find out when you get to it."

"Sounds about right," she replied, smirking, and looked back at the map again. "Hey, wait a sec… I know where that is."

He pulled the map back, and stared at it, looking for what she had seen. "You do? Where?"

"There." She reached out over his shoulder to the map and brushed an area marked as ocean with the tip of her finger. It left a small wet stain on the paper. "Just in the middle of those islands- see? I go there sometimes." She wrinkled her nose. "Haven't seen any 'fabulous treasures', though…"

"It's hidden fairly deep," the Doctor replied absently. "You wouldn't have, unless you looked specifically…"

She brightened, sitting up, and her tail flicked briefly in excitement. "I could go back!"

"Hm?" He looked up, and flapped a hand vaguely in her direction. "No, no, I absolutely forbid it. It's far too dangerous, and besides…"

"Besides what?" Ace demanded. "I go there practically every day, and it's not like it'll be any different. I can go and get the 'fabulous treasure'- whatever it is- and bring it back. No problem!"

He tapped a finger against his lips, and smiled. "Well, if you insist…"

She glared at him suspiciously for a moment. "…were you planning this as well?"

"No," he said, far too quickly. "No, of course not."

The suspicious glare continued.

"How could I have possibly known that you'd be here?" he pointed out. "This sort of occurrence is highly improbable, and I doubt that anyone, even me, could have predicted it. In any case, I'm not the sort of person to go around, tricking young ladies such as yourself into helping my admittedly rather exciting causes."

"I'm no lady," muttered Ace, but she was smiling. "All right, Professor. I'm convinced." She rubbed her hands together. "Let's go find a 'fabulous treasure'."

He reached down, and tapped her nose. She looked startled, but her smile widened quite a bit. "But there are three rules."

"There always are," she sighed.

"One," he said with a raised eyebrow and a challenging look. "I'm in charge."

"Whatever you say, Professor."

"Two, I'm not the Professor, I'm the _Doctor_ ," he continued, and Ace rolled her eyes.

"Whatever you want," she replied in a way that made it seem an awful lot like she was going to start calling him 'Professor' at the next opportunity for no real reason.

"And the third…." He trailed off, and stared out over the ocean. The sun was rising in the sky, and the clouds that had previously been covering most of the horizon were gradually dissipating and clearing up. "Well," he concluded. "I'll think up the third by the time I bring my boat around the island."

"Sure you will," she said, grinning, and then her eyes widened. "You have a boat?"

He stood up, brushing himself off. "You didn't honestly think I was going to let you go out alone?" He waggled a finger in her direction. "Remember, I have the map. And I'm in charge."

Ace seemed to consider this new turn of events for a moment, and then she shrugged. "Sure- I don't mind. It'll be nice to have someone to talk to, for once."

"Excellent," he beamed, and began to walk off. "In that case, I'll be right back. Oh, and Ace?"

"Yeah?"

He stopped; his back to her. "I did mean it when I said that you were quite extraordinary."

There was a long silence, and for a moment he thought that she wasn't going to respond. Then she cleared her throat, and coughed a bit. "You aren't so bad yourself, Professor."

He smiled at that, and set off towards his boat once more.

* * *

 **The End**


End file.
